A gas dissolving apparatus is known which has a gas dissolving tank, and injects a mixed fluid of a gas and a liquid into the tank so as to stir and thereby disperse and dissolve the gas in the liquid (refer to e.g. Japanese Laid-open Patent Publication 2004-290803). The gas dissolving tank of such a conventional gas dissolving apparatus is large and occupies a large installation space. Thus, there has been proposed a small gas dissolving apparatus which does not require a large tank, thereby achieving space reduction. This gas dissolving apparatus uses a tubular container containing or storing a gas and a liquid, and a mixed fluid of the gas and the liquid is further injected into the tubular container and stirred so as to disperse and dissolve the gas in the liquid. The thus stirred fluid is discharged from an outlet provided on the bottom of the tubular container.
However, the gas dissolving apparatus with such a tubular container has problems. For example, if the tubular container is placed with the length direction thereof being parallel to the horizon, it is true that the gas and the liquid form a long interface therebetween which extends over the entire length of the tubular container, and which thus has a large area to promote the dissolution of the gas into the liquid. However, the depth of the liquid contained or stored in the tubular container is shallow, such as about the radius of the cross-section of the tubular container cut by a plane perpendicular to the length of the tubular container, so that the gas-liquid mixed fluid is likely to be discharged from the tubular container before the gas is well dispersed and dissolved in the liquid, or while the gas in the liquid is present in the form of many large gas bubbles. On the other hand, if the tubular container is placed with the length direction thereof being perpendicular to the horizon, the gas and the liquid form a small-area interface with, at maximum, about an area of the cross-section of the tubular container cut by a plane perpendicular to the length of the tubular container, resulting in less dissolution of the gas into the liquid, although the depth of the liquid contained in the tubular container is deep enough to prevent the gas-liquid mixed fluid from being discharged while the gas in the liquid is present in the form of large gas bubbles.